Magnetic Variation Calculator

Enter your true course, magnetic variation, compass deviation, and distance to calculate magnetic heading, compass heading, intercept heading, holding pattern time, and ILS glideslope altitude loss.

Created by Luis GonzalezLast updated: May 9, 2026

How to Use This Calculator

1
Enter True Course (°)
Input your intended course relative to true north in degrees (0–360°). This is typically found on aviation charts.
2
Enter Magnetic Variation (°)
Input the magnetic variation for your location. Use a negative value for West variation (e.g., -6 for 6°W) and a positive value for East variation.
3
Enter Compass Deviation (°)
Input the compass deviation from your aircraft's deviation card. Positive for easterly deviation, negative for westerly.
4
Enter Distance (NM)
Input the distance of the flight leg or approach in nautical miles (NM). This is used for holding time and altitude loss calculations.
5
Review Headings and Metrics
The calculator will display your Magnetic Heading, Compass Heading, Intercept Heading, Holding Outbound Time, and Total ILS Altitude Loss, crucial for safe flight planning.

Example Calculation

A pilot is planning a flight leg with a true course of 215°. The magnetic variation is 6° West, and the aircraft's compass deviation is 2° East. The leg distance is 125 nautical miles.

True Course (°)

215

Magnetic Variation (°)

-6

Compass Deviation (°)

Distance (NM)

125

Results

221.0°

Tips

Update Deviation Cards Regularly

Compass deviation can change due to equipment changes or magnetic interference. Pilots should have their compasses swung and deviation cards updated during annual inspections or after significant electrical modifications.

Visualize the Variation Correction

Remember the mnemonic 'East is Least (subtract), West is Best (add)' when converting True to Magnetic. For converting Magnetic to Compass, remember 'Deviation East - Compass Least, Deviation West - Compass Best'.

Cross-Check with NAVAIDs

Always cross-check your calculated headings with available navigation aids (NAVAIDs) like VORs or GPS. This helps verify your calculations and provides a critical layer of safety in flight.

The Magnetic Variation Calculator is an essential tool for pilots and drone operators, providing critical calculations for magnetic heading, compass heading, intercept heading, holding times, and ILS altitude loss. Accurate navigation is paramount in aviation, where a single degree of error can lead to significant off-course deviations over long distances. For instance, a standard 3° glideslope for an Instrument Landing System (ILS) requires a precise descent rate of 318 feet per nautical mile, underscoring the need for exact figures in 2025 flight planning.

The Formulas for Precise Aeronautical Headings

This calculator combines several key navigational formulas. It first converts your True Course to Magnetic Heading by applying the local Magnetic Variation (subtracting West variation, adding East). Then, it converts the Magnetic Heading to Compass Heading by applying the aircraft's Compass Deviation. The Intercept Heading is calculated by adding a standard 30° to the Compass Heading for a common intercept angle. Holding Outbound Time is determined by altitude (implied by distance), and ILS Altitude Loss is derived from the standard glideslope descent rate per nautical mile.

Magnetic Heading = (True Course - Magnetic Variation) (normalized 0-360°)
Compass Heading = (Magnetic Heading - Compass Deviation) (normalized 0-360°)
Intercept Heading = (Compass Heading + 30°) (normalized 0-360°)
Total ILS Altitude Loss = 318 ft/NM × Distance (NM)

Note: Magnetic Variation is negative for West, positive for East. Compass Deviation is positive for Easterly, negative for Westerly.

💡 For another critical flight parameter, our True Airspeed (TAS) Calculator helps pilots understand their actual speed through the air.

Planning a Flight Leg with Magnetic Variation

Consider a pilot planning a flight leg with a True Course of 215°. The magnetic variation at their location is 6° West (entered as -6°), and the aircraft's compass deviation is 2° East (entered as 2°). The leg distance is 125 nautical miles.

Calculate Magnetic Heading: 215° True Course - (-6° West Variation) = 221° Magnetic Heading.
Calculate Compass Heading: 221° Magnetic Heading - (2° East Deviation) = 219° Compass Heading.
Calculate Intercept Heading: 219° Compass Heading + 30° = 249° Intercept Heading.
Calculate Holding Outbound Time: For 125 NM, which is above 14 NM, the standard is 1.5 minutes.
Calculate Total ILS Altitude Loss: 318 ft/NM × 125 NM = 39,750 ft.

The pilot would steer a Compass Heading of 219° and be prepared for a significant descent on a 125 NM ILS approach.

💡 To fine-tune your navigation using ground-based aids, our VOR Radial to Heading Calculator assists in translating VOR readings into steerable headings.

Navigating with Precision in Aviation

In aviation, navigating with precision is not just about reaching a destination; it's a critical safety imperative. Pilots must constantly account for the discrepancies between true north (used on charts), magnetic north (what a compass points to), and the aircraft's internal magnetic interference (compass deviation). These calculations are vital for flight planning, especially for Instrument Flight Rules (IFR) procedures where visibility is limited and reliance on instruments is absolute. A small error in calculating magnetic variation or compass deviation can lead to significant off-course errors, potentially placing an aircraft outside its intended corridor or even into hazardous airspace. Adhering to FAA guidelines and consistently applying these corrections ensures that pilots can maintain their intended flight path and execute precise approaches.

Pilot Interpretation of Heading Errors

Experienced pilots constantly interpret and manage heading errors to maintain an accurate course. They understand that magnetic variation, published on aeronautical charts, is a geographical constant for a given area, while compass deviation is unique to each aircraft and its current magnetic heading, documented on a deviation card. A pilot will typically cross-reference their magnetic compass with other navigation systems like a Horizontal Situation Indicator (HSI) or GPS, which often display true or magnetic headings directly. If a discrepancy exists, they first check for known errors (like an uncompensated deviation) and then consider external factors (e.g., magnetic anomalies, electrical interference). For instance, a consistent 3-5 degree error might prompt a recalculation of variation or a re-evaluation of the deviation card, as even small, persistent errors can lead to being significantly off-track after an hour of flight.

Frequently Asked Questions

What is magnetic variation and why is it essential for pilots?

Magnetic variation (also known as magnetic declination) is the angular difference between true north and magnetic north at a specific location. It is essential for pilots because aviation charts are referenced to true north, while an aircraft's magnetic compass points to magnetic north. Pilots must apply the correct magnetic variation to convert true courses into magnetic headings for accurate navigation, preventing significant errors, especially on long cross-country flights.

What is compass deviation and how does it affect heading?

Compass deviation is the error introduced into a magnetic compass reading by magnetic fields originating from the aircraft itself, such as electrical currents, ferrous metals, or electronic equipment. This deviation varies with the aircraft's heading. Pilots use a 'deviation card' (found near the compass) to correct for these errors, converting the magnetic heading into a compass heading that accounts for the aircraft's internal magnetic interference, ensuring an accurate steerable course.

How does an Instrument Landing System (ILS) glideslope work?

An Instrument Landing System (ILS) glideslope provides vertical guidance to pilots during an instrument approach, helping them descend at the correct angle towards the runway touchdown zone. It transmits a very high frequency (VHF) signal that creates a narrow beam, typically at a 3-degree angle from the horizontal. Aircraft instruments interpret this signal, indicating whether the aircraft is above, below, or on the correct descent path, ensuring a safe and precise landing.

Why do holding patterns have specific inbound and outbound times?

Holding patterns are standardized flight procedures used to delay aircraft in flight, typically near an airport or navigation fix. The specific inbound and outbound leg times (usually 1 minute for altitudes up to 14,000 feet, and 1.5 minutes above 14,000 feet) are designed to make the pattern predictable and manageable for air traffic control. These timings ensure that each circuit of the holding pattern takes a consistent amount of time, allowing for efficient sequencing of aircraft.